The present invention relates to a flexible metal sealing joint or gasket having expendable projecting portions making it possible to rapidly obtain a good sealing action for a limited clamping or tightening force.
More specifically, the present invention relates to a flexible metal sealing joint of the type having at least one elastic metal core which, in the rest position, is shaped like a torus and at least one outer envelope made from a ductile material, in which is inserted said metal core.
It is pointed out that the invention can be used in all joints of this type and independently of the shape thereof (rectangular, circular, oblong, triangular, oval, etc.). In addition, it relates to joints having one sealing line and to those having two sealing lines.
In existing metal joints, the toroidal elastic core is constituted either by a metal tube, or by a helical spring having contiguous turns and closed on itself. In the latter case, the section of the wire constituting the spring can be of a random nature and is in particular circular, rectangular or circular segmental. The tube or the helical spring, fixed to the edge, imparts the elasticity to the joint.
Moreover, the envelope or envelopes surrounding the core of existing joints are made from plated materials or thin sheets, of e.g. polytetrafluoroethylene, aluminium, silver, copper, nickel, tantalum, stainless steel, zirconium, etc.
When the joints comprise several envelopes, each of the latter has a special function. Thus, when the core of the joint is constituted by a spring having contiguous turns, the inner envelope generally has a load distribution function at each apex of the turn of the elastic core. The outer envelope is made from a ductile material which, due to its creep capacity in contacting surface roughnesses, makes it possible to give the joint a perfect seal when fixed in an assembly. In general terms, the envelopes of the joint are characterized by the plastic properties of the materials forming them.
For further details regarding the structure of a metal sealing joint, whose core is constituted by a helical spring having contiguous turns, reference should be made to French Patent No. 73 19488 of May 29th 1973 in the name of the Commissariat a l'Energie Atomique.
Industrial experience has shown that the elastic metal joints make it possible to obtain a particularly good static sealing action and in particular an excellent thermal behaviour.
In addition, static metal joints are known, which have a solid part, e.g. of aluminium or copper, whose bearing faces are provided with one or more projecting portions having a triangular or circular arc-shaped cross-section. In joints of this type, so-called solid knife-edge joints, the reduction of the surfaces of the joint in contact with the facing portion of the assembly makes it possible to reduce the tightening or clamping force necessary for obtaining the desired seal. However, these joints suffer from the disadvantage of being very sensitive to thermal creep, so that the reliability of the seal is not ensured.